When the Beatles arrived in the United States 50 years ago this month, already full-blown stars in their native England, they rewrote the rules of pop music and how we treat its prime movers. Sure, the girls squealed for Frank Sinatra in the 1940s and Elvis Presley a decade later, but on Feb. 9, 1964, the Beatles sent shock waves through America’s popular culture when they debuted on “The Ed Sullivan Show.”

On the 50th anniversary of that pivotal televised moment, it’s worth asking: What changed that day, and what other changes were underway on the music scene that would combine to make rock ’n’ roll the true cultural force it became?

As the Beatles, Paul McCartney, John Lennon, George Harrison, and Ringo Starr were a perfect storm for the times. They wrote their own songs, which had the tender harmonies of the catchiest hits to come out of the Brill Building. They played their own instruments — jangly guitars with lines that echoed their favorite R&B records. They looked like cherubs in their suits and boots and sang right to those girls who sobbed at the sight of them. And those haircuts. They were game, and eager, for the massive success that awaited them.

Sure enough, it happened. Beatlemania ushered in the British Invasion, a tidal wave that brought with it the Rolling Stones, the Kinks, the Who, Herman’s Hermits, and blue-eyed soul singers such as Dusty Springfield.

One of the more fascinating new books on the Fab Four’s impact is “The Beatles Are Here!,” a collection of essays and oral accounts curated and edited by Penelope Rowlands and featuring a range of writers (Greil Marcus, Fran Lebowitz) and musicians (Billy Joel, Cyndi Lauper).

‘We were kind of whipped into a frenzy by the really powerful disc jockeys of the era.’

The book’s cover photo, originally published in The New York Times in 1964, is an iconic image of girls losing their minds over the foursome, holding a sign emblazoned with “Beatles Please Stay Here 4-Ever.” The girl in the middle, the one who appears to be crying, is Rowlands.

“Somebody asked me, ‘What were you girls thinking?’ and I thought that was a curious way to put it, because I’m sure thinking didn’t enter into the situation,” Rowlands says of that photo. “It just seemed to be pure emotion. In doing this book, I began to remember that we heard about the screaming girls in England before we ever heard the Beatles’ music.”

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From left: Paul McCartney, George Harrison, and John Lennon. Ringo Starr is on drums.

“We were kind of whipped into a frenzy by the really powerful disc jockeys of the era,” she adds. “Murray the K and Cousin Brucie were the two who dominated the airwaves where I grew up in New York.”

A recurring theme in the book is the notion that before the Beatles arrived, pop music was lying fallow, with a nation still plunged in grief over John F. Kennedy’s assassination the year before. The country was hungry for new voices, a splash of Technicolor on an otherwise gray canvas.

The Beatles’ timing couldn’t have been better. After the first generation of rock ’n’ rollers (Presley, Little Richard, Jerry Lee Lewis) had crested, the landscape was wide open. The charts were full of sweet girl-group pop (the Shirelles, the Chiffons), surf bands (the Beach Boys, Jan and Dean), and the last leg of acts that Mom and Dad loved (Andy Williams, Bobby Vinton).

Meanwhile, Bob Dylan had already released two albums, and the title track of his first album in ’64 seemed to speak to the spirit of the year: “The Times They Are A-Changin’.”

Then, of course, there was Motown, which truly hit its stride with groups like the Supremes, the Temptations, and Sam Cooke, who that year released “A Change Is Gonna Come,” a rallying cry of the civil rights movement. The Supremes became full-fledged stars in 1964 with “Baby Love,” “Come See About Me,” and “Where Did Our Love Go.”

Mark and Colleen Hayward

The music of the Beatles on “The Ed Sullivan Show,” the Supremes (pictured), and Lesley Gore made waves in 1964.

“It was a time of change, major change,” says Mary Wilson, a founding member of the Supremes, in a recent phone interview. “The world was starting to open up its borders, and people were going to new places they never dreamed of. It was a huge year.”

Wilson mentions the importance of “The T.A.M.I. Show,” a seminal concert film taped in 1964 that featured the Supremes, Chuck Berry, the Beach Boys, Marvin Gaye, the Stones, and, most memorably, James Brown. Wilson says it was proof that pop music was finally bestowing mainstream recognition on artists who had already been famous in the black community.

“People tend to talk about the Beatles in ’64 as though absolutely everybody was swooning over them, when in fact it was probably white America that was swooning over them,” says John Platoff, a professor of music at Trinity College in Hartford who teaches a seminar on the Beatles and the 1960s. “I don’t think African-American young people were unaware or utterly indifferent, but I don’t think they had at all the same reaction. You look at photos of kids going crazy over the Beatles, and you don’t see black faces.”

For Martha Reeves, the music that came out of 1964 wasn’t about skin color; it was universal.

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Lesley Gore.

“When I first got into show business, there was no white or black music,” Reeves says from her home in Detroit. “There was just music that everybody enjoyed, and Motown was not an all-black company. Our music had no color on it. It was made for people who enjoyed music, and our music will last forever because it was family-oriented.”

In last year’s book “Ready for a Brand New Beat: How ‘Dancing in the Street’ Became the Anthem for a Changing America,” author Mark Kurlansky used the Martha Reeves and the Vandellas hit as a symbol of how ’64 was notable for so many reasons beyond the British Invasion.

“I don’t think people are aware of the impact of the black freedom struggle on popular music,” says Kurlansky, the author of bestsellers such as “Salt” and “Cod.” “If there hadn’t been that movement, there wouldn’t be rock ’n’ roll.”

Lesley Gore was another artist making waves in 1964. She was 17 when the Beatles arrived on these shores and had already had a No. 1 hit the previous year with “It’s My Party.” In ’64, she had her second biggest song, the one that has resonated as one of pop music’s first hits with an overtly feminist message. “You Don’t Own Me” was a new breed of song for a female artist: “You don’t own me/I’m not just one of your many toys.”

“When I first heard that song, I didn’t immediately think of feminism, but I did think of humanism,” Gore says. “It was a great song to be 17 years old and stand up in front of an audience and shake your finger and say, ‘You don’t own me.’ The feminists picked it up as their anthem, which is great, but I consider it a little more than just feminism. I think everyone can sing that song and mean it, like so many other songs from that era.”